It is essential that a container closure of the shape described above have a synthetic resin liner which may be positioned on the underside of the shell to obtain a tight seal with a container opening. In Japanese Patent Gazette Item 53-65184 (1978) which is also Japanese Laid Open Patent Application No. 51-13773 which is one of the priority applications of U.S. Pat. No. 4,114,775, a container closure having this shape is disclosed and includes an outer circular projecting rim forming an inner circumference surface that is adhered to the outer circumference surface of the container opening when tightly sealed and a liner press-molded to the inner surface of the metal shell where the liner includes an inner circular projecting rim which has an outer circumferential surface that adheres to the inner circumferential edge of the container opening for the purpose of improving sealing characteristics. A container closure possessing this kind of liner configuration has improved sealing characteristics in comparison to container closures with previously proposed liner configurations as described in the above-mentioned patent gazette item.
However it has been found that a decline in the tight sealing characteristics developes when a fairly large impact is inflicted to a container closure that has the above-mentioned liner configuration.
An improved liner that can maintain tight sealing characteristics even with the infliction of a fairly large impact is disclosed in U.S. application Ser. No. 208,398, filed Nov. 19, 1980, now U.S. Pat. No. 4,379,512, assigned to the same assignee as this application. The liner disclosed has a first circular projecting rim which provides an inner circumferential surface that adheres to the outer circumferential surface of a container opening to seal tightly and has a second circular projecting rim which adheres to the top surface of the container opening and is arranged so as to be positioned opposite the top surface of the opening at the inside of the first circular projecting rim. It is disclosed in the patent that the height of the second circular projecting rim is somewhat less than the height of the first circular projecting rim.
It has now been found, however, that the height of the second circular projecting rim should be greater than the height of the first circular projecting rim in order to increase the anti-impact capability of the closure. Further, it has been found that if the height of the second circular projecting rim is greater than the height of the first circular projecting rim, that any decrease in the tight seal characteristic due to the so-called "doming" phenomenon of the container closure (the phenomenon where the container closure surface changes shape by protruding upward due to the existence of pressure within the container) can be prevented with greater certainty.
It is therefore an object of the invention to provide for a container closure having a liner including at least circular projecting rims where a radially inner rim has a greater height than a radially outer rim in order to increase impact resistance and reduce loss of sealing characteristics due to "doming".